Profile-based CPU controls to save power / improve perf

In order to save more power and hence improve on-battery life, in Ubuntu, CPU governor as well as clock speeds can be controlled more finely using cpufreqd. To illustrate how this can be useful, my ThinkPad X201 (running Ubuntu 14.04), always uses performance governor although the laptop isn't being plugged to wall-charger. What a waste of power! cpufreqd allows different profiles to be set,depending on the charging status or battery-level. In a particular profile, CPU governor as well as min/max CPU clock can be customized. Moreover, there's also indicator-cpufreq, which provides a nice status bar icon indicating current CPU configuration (both governor and speed).

Here's how to get them up and running:
1. sudo apt-get install indicator-cpufreq cpufreqd cpufrequtils
2. sudo vim /etc/cpufreqd.conf # This is the file to configure the profile

Below is snippet of what I modified (the rest stays default):

[Profile]
name=Performance High
minfreq=70%
maxfreq=100%
policy=performance
#exec_post=echo 8 > /proc/acpi/sony/brightness
[/Profile]

[Profile]
name=Performance Low
minfreq=60%
maxfreq=80%
policy=performance
[/Profile]


Furthermore, the followings are useful for debugging:
1. cpufreq-info. This can be used to see what governor and clock are currently running. Also useful to see whether the configuration selected via indicator-cpufreq (e.g. manually choosing a different governor) is applied fine. In the past, I've had issue where my CPU clock was locked to 1.2GHZ (this was back on Ubuntu 12.04, for further detail, see my other blog post)

2. 'cat /var/log/syslog', as cpufreqd logs are written onto this.

3. [Added 10/21/2015] If for some reasons, the rules written under /etc/cpufreqd.conf doesn't get applied, check if cpufreqd daemon is actually running. If it's not, you can start it manually through sudo '/etc/init.d/cpufreqd start'. On my Thinkpad X201, without cpufreqd running, its max frequency is somehow capped in a weird manner.